Determinants of marginal gap of single crowns before cementation: An umbrella review

Marginal fit is a key determinant of crown success. Variable marginal gap values have been reported in the literature, referencing multiple contributing factors. A consolidated analysis of systematic reviews is required to clarify the reports.

The purpose of this umbrella review was to quantitatively synthesize findings from systematic reviews of in vitro studies that evaluated marginal gaps and assessed the influence of the crown type, crown fabrication material, measurement instrument, abutment tooth material, tooth type, and crown fabrication method on the marginal gap.

The search was conducted in June 2025 using the EBSCO Host, Scopus, PubMed, and Web of Science databases following the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines and predefined eligibility criteria. Eligible systematic reviews were critically appraised using the Joanna Briggs Institute (JBI) Critical Appraisal Checklist. Umbrella analyses were performed using the Welch test for unequal variances, the Games Howell post hoc test, and multiple regression adjusted with robust clustered standard error and the Wald test for robust model-level evaluation (α=.05).

Seventeen systematic reviews, reporting a mean marginal gap of 79.4 ±22.8 µm were included. No significant differences were observed in mean marginal gap across different crown types (F=0.37, P=.775) or crown fabrication materials (F=0.48, P=.784). Crowns assessed using the impression replica instrument showed significantly larger marginal gaps (β=37.86, P<.001) compared with microscopy. No significant differences were found between the marginal gaps of crowns fabricated using conventional (88.0 ±35.0 µm) and computer-aided design and computer-aided manufacturing (CAD-CAM) (80.3 ±35.0 µm) methods across crown types (F=1.00, P=.319).

Crown type, crown fabrication material, and crown fabrication method demonstrated no significant effect on marginal gaps. The impression replica instrument overvalued marginal gaps in comparison with microscopy. Based on the results of this study, the contemporary acceptable limit for in vitro crown marginal gap is 120 µm.